The present invention relates to an electron beam lithographic apparatus for the fabrication of semiconducter devices and more particularly to such a system in which the wafer to be exposed is held by and traversed with respect to the electron beam by an air bearing supported puck. The apparatus can also be used to form precision reticles used in more conventional lithographic processes.
In its ongoing effort to create increasingly complex integrated circuit devices, the semiconductor industry has moved toward ever finer device geometries. The detail has become so fine, in fact, that the resolution required for lithographic processes is beginning to go beyond the defraction limits imposed by the use of visible or even ultraviolet light. Accordingly, systems are being developed which utilize electron beams or x-rays to effect the exposure of the lithographic resists which are used for the manufacture of semiconducter devices. However, while lithographic exposure with light can occur under atmospheric pressure, electron beam lithography must occur in a high vacuum. Further, since the area which can be scanned and exposed by an electron beam operating at high resolution is highly limited, i.e. a region much smaller than that of the typical semiconducter wafer, it is necessary to physically move the wafer to be exposed in relation to the electron beam source in order to expose different regions on the wafer's surface.
While a straightforward solution of this problem would be to place the wafer moving mechanisms within the vacuum system, this is unattractive in practice since these mechanisms typically involve lubricants and organic compounds which can degrade the vacuum and quickly poison the electron emissive cathode employed to generate the electron beam. Accordingly, it is deemed preferable that the stage or other means for carrying the semiconducter wafer extend outside of the vacuum chamber for connection to the mechanical drive mechanisms.
Similarly while airbearings have been widely used for supporting both semiconducter wafers and various mechanism elements including X-Y stages, the use of such bearings in connection with vacuum systems has not been widely accepted not only because the vacuum pumping requirements are increased by the gas introduced through the air bearing, but also because the atmospheric pressure opposing the vacuum has typically placed both an unacceptable heavy mechanical load on the system. The atmospheric load places strains on the moving parts which, no matter how heavily constructed, exhibit some distortion. This distortion interferes understandably with the precise positioning of the semiconducter wafer being carried by the mechanism. Further, since the moving parts subjected to the vacuum must be strongly and heavily constructed, they cannot easily be moved at the high speed which is highly desirable in order to effect rapid repositioning of a semiconducter wafer in order to obtain maximum throughput of the lithographic machine.
Among the several objects of the present invention there may be noted the provision of an electron beam lithographic system for the manufacture of semiconducter devices; the provision of such a system which provides rapid and precise positioning of a semiconducter wafer with respect to an electron beam source; the provision of such a system in which the wafer transporting stage may be of relatively light construction to facilitate rapid positioning and reasonable power requirements; the provision of such a system in which facilitates the maintenance of a high vacuum in the environment of the electron beam source; the provision of such a system which does not subject the wafer carrying stage to heavy distorting forces; the provision of such a system in which the wafer carrying stage may be moved without substantial friction; the provision of such a system which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.